Abstract
As one of the leading acceleration mechanisms in laser-driven underdense plasmas, direct laser acceleration (DLA) is capable of producing high-energy-density electron beams in a plasma channel for many applications. However, the mechanism relies on highly nonlinear particle-laser resonances, rendering its modeling and control to be very challenging. Here, we report on novel physics of the particle resonances and, based on that, define a potential path toward more controlled DLA. Key findings are acquired by treating the electron propagation angle independently within a comprehensive model. This approach uncovers the complete particle resonances over broad propagation angles, the physical regimes under which paraxial/non-paraxial dynamics dominates, a unified picture for different harmonics, and crucially, the physical accessibility to these particle resonances. These new insights can have important implications where we address the basic issue of particle trapping as an example. We show how the uncovered trapping parameter space can lead to better acceleration control. More implications for the development of this basic type of acceleration are discussed.
Highlights
Utilizing high-power lasers for high-energy electron acceleration in plasmas has been intensely pursued in the last few decades [1,2]
Two major types of acceleration have been exploited: direct acceleration by the laser fields [3] and indirect plasma-field acceleration induced in the laser wake [4]
Tremendous efforts have been devoted to controlling electron trapping in the wakefield with suitable laser-plasma conditions [5,6,7], which have led to high-quality generation of pC-charge GeV electron beams [8]
Summary
Utilizing high-power lasers for high-energy electron acceleration in plasmas has been intensely pursued in the last few decades [1,2]. Trapped electrons are subject to the overlapping laser fields, such that DLA is invoked by particle-laser resonances when the betatron oscillation matches witnessed laser oscillation [3] This process represents a strong laser-electron coupling and produces high-current electron beams of enormous nC-μC charge [9], which can drive ion acceleration and high-dose x=γ-rays, neutrons, and positrons for medical, nuclear, and radiography applications [10,11,12,13,14]. Basic questions like whether nonparaxial dynamics exists, what physical regimes each refers to, how the first and high-order resonances are correlated, and crucially, what determines their accessibility remain unclear These gaps have left some basic elements for controlling DLA yet to be well defined. We apply the results to particle trapping and show how better design of DLA may be pursued based on the uncovered trapping parameter space
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